As is generally known, a blow-by processing device is provided for processing blow-by gases leaked from combustion chambers of an internal combustion engine into a crankcase (see Patent document 1). The blow-by processing device is configured for introducing fresh air through a fresh-air introduction gas route, which is connected to the throttle upstream part of an intake passage, into the crankcase for ventilation, and for supplying blow-by gases in the crankcase through a blow-by gas reflux gas route, which is connected to the throttle downstream part of the intake passage, into the intake passage and for returning back into the combustion chambers for combustion processing. Also provided is a PCV (positive crankcase ventilation) valve installed in the blow-by gas reflux gas route for adjusting or regulating the rate of blow-by gas flow. By the way, once the amount of blow-by exceeds the flow rate of the PCV valve in a high load range, the excess blow-by gases are also allowed to be supplied via the fresh-air introduction gas route into the intake passage.
Also, to prevent oil (oil mist) in blow-by gases from being carried or pulled into the intake system, separators (oil separators) are disposed or arranged in the respective gas routes for separating oil mist in the blow-by gases.